import java.util.Objects;

public class ObjectTest {
    static ObjectTest obj=null;

    public static void main(String[] args) {
        System.out.println(Objects.hashCode(obj));
        System.out.println(Objects.toString(obj));
        //System.out.println(Objects.requireNonNull(obj,"no null!"));
        String a ="a";

        System.out.println(a.compareTo("d"));

    }
}
